Are you asking about the size of their fleets??? If so you can get the info on the airlines websites.
As of right now AA has the larget fleet of the U.S. based carriers as well as the larget of any airline, around 900 aircraft.

"On October 22, 2001, United announced that its entire fleet of 611 aircraft are now equipped with the new cockpit security bars in compliance with the FAA's new guidelines. United's employees worked literally around-the-clock to install the security bars on the airline's entire operating fleet. "

Northwest has a total of 506 jet aircraft including the ARJ's and the CRJ's. Not included are the Mesaba SF340's.
http://ir.nwa.com/ireye/ir_site.zhtml?ticker=NWAC&script=11906&layout=7&item_id='fleet.htm'

"Air Canada provides scheduled and charter air transportation for passengers and cargo to more than 150 destinations on five continents. Canada's flag carrier is the 10th largest commercial airline in the world and serves more than 30 million customers annually with a fleet consisting of more than 300 aircraft. Air Canada is a founding member of Star Alliance providing the world's most comprehensive air transportation network."